The present invention relates to saw chains, and in particular, to an anti-kickback saw chain.
The usual type of chain saw has an elongate saw bar terminating at a rounded nose, and an endless saw chain which is driven in a grooved track about the periphery of the bar. The saw chain is composed of a series of center links which are pivotally joined by a series of side links and by a series of left and right cutter links disposed alternately on opposite sides of the chain at regular intervals therealong. Each cutter link has a cutter blade with a forward cutting edge and a depth gauge disposed forwardly of the cutter blade and extending somewhat below the height of the cutter edge, to produce a desired depth of cut, or depth of bite, of each cutter blade into the workpiece.
A safety hazard associated with the use of chain saws is what is commonly referred to as kickback. This refers to the tendency of a cutter portion in a cutter link of a saw chain to dig into the wood as the cutter link moves over the upper quadrant of the nose of a saw bar. When this occurs, and with movement of the cutter link abruptly stopped or seriously impeded, reaction forces produced tend to force the bar of the chain saw upwardly and rearwardly into the face of the operator.
A number of saw chains designed to prevent the problem of kickback are disclosed in the prior art. Many of the known anti-kickback chains employ safety links which are placed in the chains at positions preceeding the chain cutter links. Each safety link has an upstanding tang or cam portion which extends radially outwardly when the safety link is traversing a rounded saw bar nose to reduce the effective depth gauge setting for the trailing cutter link.
One general object of the present invention is to provide a novel safety link which, when incorporated into a conventional saw chain, produces an anti-kickback chain having several advantages not found in prior art anti-kickback saw chains.
More specifically, it is an object of the invention to provide such a safety link having leading and trailing projections which cooperate in a saw chain to eliminate kickback.
Another object of the invention is to provide such a safety link having projections which are easily filed in a saw chain filing operation.
Yet another object of the invention is to provide such a safety link which is relatively lightweight.
Providing an anti-kickback saw chain employing such a safety link is still another object of the present invention.
An anti-kickback saw chain constructed according to the present invention includes a series of left and right cutter links disposed alternately on opposite sides of the chain, and for each cutter link, a center link pivotally joined to the forward end of the cutter link and a safety link pivotally joined to the forward end of the center link on the side of the chain opposite the trailing cutter link. Each cutter link includes the usual depth gauge and cutter blade. The safety link includes a leading projection adjacent its forward end and a trailing projection adjacent its rear end, the leading and trailing projections being separated by a gullet disposed intermediate the projections.
In a straight portion of the chain, the leading and trailing projections extend substantially no higher than the depth gauge in the trailing cutter link, and the trailing projection also projects rearwardly to overlap the depth gauge laterally. The leading projection in the safety link projects upwardly in the chain substantially no higher than the rear end of the cutter blade in the cutter link which is immediately in advance of the safety link. In a portion of the chain traversing the rounded nose of a saw bar, the safety link pivots outwardly to a position where the trailing projection extends above the height of the depth gauge in the trailing cutter link, to reduce the effective depth gauge setting in that link.
These and other objects and features of the present invention will become more fully apparent when the following detailed description of a preferred embodiment of the invention is read in connection with the accompanying drawings.